Physics Chapter 2 Questions
What is the net force on an object in either static or dynamic equilibrium?
0
What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?
0.
What is the resultant of a pair of 1 pound forces at right angles to each other?
1.41=c
Henry Heavyweight weighs 1200 N and stands on a pair of bathroom scales so that one scale reads twice as much as the other. What are the scale readings?
400 and 800 on the other.
A different scaffold that weighs 400N supports two painters, one 500 N and the other 400N. The reading in the left scale is 800 N. What is the reading in the right hand scale?
500N
If the strong man in the preceding exercise exerts a downward force of 800 N on the rope, how much upward force is exerted on the block?
800N
Nellie hangs motionless by one hand from a clothesline. Which side of the line, a or b, has the greater tension?
A.
Why do we say that force is a vector quantity?
Because it requires both magnitude and direction
If you're in a car at rest that gets hit from behind, you can suffer a serious neck injury called whiplash. What does whiplash have to do with Newton's first law?
Before the wreck your body will be going forward at the same speed as the car, so when the crash happens that forward motion will be distrupted, causing the body to be pushed backwards, and the head rest is there to stop the head/neck from snapping backwards too far.
Three pucks A, B, C are shown sliding across ice at the noted speeds. Air and ice friction forces are negligible.
C, B, A
Rank the net forces on the blocks from least to most in the four situations, A,B,C and D. 10N-A-5N, 7N-B-3N, 12N-C-4N, 3N-D-3N
D, B, A, C
State the equilibrium rule for forces in symbolic notation.
EF=0
When a ball is tossed straight up, it momentarily comes to a stop at the top of its path. Is it in equilibrium during this brief moment? Why or why not?
For a brief second it is at equilibrium because it wouldn't stop if there wasn't an outside force acting on it, and in order for it to fall back down the force must be greater and for it to be greater, it mst at some point for a split second be equal.
A ball rolling along a floor doesn't continue rolling indefinitely. Is this because it is seeking a place of rest or because some force is acting upon it? If the latter, identity the force.
Force of friction is acting upon it. It will continue until an outside force acts upon it.
Was it Galileo or Newton who first proposed the concept of inertia?
Galileo
What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?
He discovered that Aristotle's theory that the more mass something has, the faster it falls. Galileo found that no matter what the mass is, that everything falls at pretty much the same rate.
What Aristotelian idea did Galileo discredit in his fabled Leaning Tower demonstration?
He discreited the idea that objects twice as heavy will fall twice as fast
In tearing a paper towel or plastic bag from a roll, why is a sharp jerk more effective than a slow pull?
If you were to have a slow continuous motion the roll would keep on going, but with a stronger quick jerk, it causes disruption and causes the paper to rip.
Is inertia the reason for moving objects maintaining motion or the name given to this property?
It is the name given to the property.
Suppose that you're in a moving car and the motor stops running. You step on the brakes and slow the car to half speed. If you release your foot from the brakes, will the car speed up a bit, or will it continue at half speed and slow due to friction? Defend your answer with your discussion partners.
It will continue at half speed and slow due to friction because of the law of inertia.
If you toss a coin straight upward while riding in a train, where does the coin land when the motion of the train in uniform along a straight-line track? When the train slows while the coin is in the air?
It will land in your hand. It will land in front of you
In order to slide a heavy cabinet across the floor at constant speed, you exert a horizontal force of 600 N. Is the force of friction between the cabinet and the floor greater than, less than, or equal to 600 N? Defend your answer.
The force of friction will be equal to the horizontal force of 600 N because in order for it to slide at a constant speed, there must be an equilibrium between the two forces.
Consider the normal force on a book at rest on a table. If the table is tilted so that the surface forms an inclined plane, will the magnitude of the normal force change? If so, how?
The magnitude changes it becomes less
What state of motion did Aristotle attribute to Earth?
Natural motion
Two people each pull with a force of 300 N on a rope in a tug-of-war. What is the net force on the rope? How much force is exerted on each person by the rope?
Net force is zero. 300 N.
Your friend sits at rest on a chair. Can you say that no force acts on her? Or is it correct to say that no net force acts on her? Defend your answer.
No net force is acting on her because the force downward (gravity) and the force upward (support force) are equal and when they are equal, net force is zero.
A child learns in school that Earth is traveling faster than 100,000 kilometers per hour around the Sun and in a frightened tone, asks why we aren't swept off. What is your explanation?
Our bodies, as well as everything else, are spinning at the same rate as the earth, and unless acted upon by an outside force we will continue to do so.
In terms of Newton's first law, how does a car headrest help to guard against whiplash in a rear-end collision?
Strongest 32N, Weakest 8N
Before the time of Galileo and Newton, some learned scholars thought that a stone dropped from the top of a tall mast of a moving ship would fall vertically and hit the deck behind the mast by a distance equal to how far the ship had moved forward while the stone was falling. In light of your understanding of Newton's first law, what do you think about this?
The stone is traveling just as fast as the person who drops it, and according to the law of inertia it will continue to move at that speed. When it's dropped it will only stop going at the same speed when it hits the ground.
An empty jug of weight W rests on a table. What is the support force exerted on the jug by the table? What is the support force when water of weight w is poured into the jug?
The support force is equivalent to the empty jug, and when the water is poured into the jug and the weight of the jug increases, the upward force will increase as well.
How many significant forces act on a book at rest on a table? Identify the forces.
Two. the downward force (gravity) and the upward force (support force), since it's at equilibrium there is zero net force.
Harry the painter swings year after year from his bosun's chair. His weight is 500 N and the rope, unkown to him, has a breaking point of 300 N. Why doesn't the rope break when he is supported as shown at the left? One day, Harry is painting near a flagpole, and, for a change, he ties the free end of the rope to the flagpole instead of to his chair, as shown at the right. Why did Harry end up taking his vacation early?
When both ends of the rope are connected to the chair, each vector is 300 N, so there is a 600 N holding up Harry who is 500 N. He falls when he connects the rope to the flag because the one vector is holding the flag at 300 N and holding him at 300 N is impossible so the rope breaks.
Each bone in the skeletal chain of bones forming your spine is separated from its neighbors by disks of elastic tissue. What happens, then, when you jump heavily onto your feet from an elevated position? Discuss why you think you are a little taller in the morning than at night.
When you jump and land on the floor, there is a downward force being exerted on the body causing discs to compress. At night no force pulling along length of spine.
The smokestack of a stationary toy train consists of a vertical spring gun that shoots a steel ball a meter or so straight into the air--so straight that the ball always falls back into the smokestack. Suppose the train moves at constant speed along the striaght track. Do you think the all will still return to the smoke stack if shot form the moving train> What if the train gains speed along the straight track? What if it moves at a constant speed on a circular track? Discuss why your answers differ.
Yes, because it will be going in a horizontal line at a steady rate. No, if it gains speed it will land behind the smoke stack. No, because it won't be moving in a straight horizontal path.
Your friend says that inertia is a force that keeps things in their place, either at rest or in motion. Do you and your discussion partners agree? Why or why not?
Yes, inertia keeps objects at rest, at rest and objects in motion, in motion until acted upon by an outside force.
As you stand on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why aren't you moved upward by this force?
Yes, the upward force exerts the same amount of force that is pushing down on it-the same as my weight. I'm not moved upward because it is equal on both sides, net force is zero.
Can force be expressed in units of pounds and also in units of newtons.
Yes.
Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?
Yes. You continue at the same speed. Inertia.
Which is more likely to break: a hammock stretched tightly between a pair of trees or one that sags more when you sit on it?
a hammock stretched tightly
The rope supports a lantern that weights 50 N. Is the tension in the rope less than, equal to, or greater than 50 N? Use the parallelogram rule to defend your answer.
equal
The rope of Exercise 56 is repositioned as shown and still supports the 50-N lantern. Is the tension in the rope less than, equal to, or greater than 50 N? Use the parallelogram rule to defend your answer.
greater
What type of path does a moving object follow in the absence of a force?
horizontal
What concept was not understood in the 16th century when people couldn't conceive of a moving Earth.
inertia
A space probe may be carried by a rocket into outer space. What keeps the probe moving after the rocket no longer pushes it?
interia
Consider a pairs of forces, one having a magnitude of 20 N and the other a magnitude of 12 N. What is the strongest possible net force for these two forces? What is the weakest possible net force?
strongest: 32N, Weakest: 8N
When you stand at rest on a bathroom scale, how does your weight compare with the support force by the scale?
their magnitudes are the same. the support force source shows your weight.
